Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.63   12.204%   $232.9692   $232.97   $232.95   $233.00  
  Purchase #2 $42.72   7.683%   $46.0022   $46.00   $46.00   $46.00  
  Purchase #3 $225.88   12.662%   $254.4809   $254.48   $254.50   $254.50  
  Purchase #4 $105.53   7.528%   $113.4743   $113.47   $113.45   $113.50  
  Purchase #5 $238.40   3.442%   $246.6057   $246.61   $246.60   $246.60  
  Purchase #6 $61.60   6.331%   $65.4999   $65.50   $65.50   $65.50  
  Purchase #7 $160.29   12.626%   $180.5282   $180.53   $180.55   $180.50  
  7 purchase totals = $1,042.05       $1,139.5604   $1,139.56   $1,139.55   $1,139.60